pgsql: Cosmetic improvements for faster column addition.

Cosmetic improvements for faster column addition.

Changed the name of few structure members for the sake of clarity and
removed spurious whitespace.

Reported-by: Amit Kapila
Author: Amit Kapila, based on suggestion by Andrew Dunstan
Reviewed-by: Alvaro Herrera
Discussion: https://postgr.es/m/CAA4eK1K2znsFpC+NQ9A4vxT4uDxADN4RmvHX0L6Y=aHVo9gB4Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8121ab88e7dfe6ebe56c58257733354cb85f092c

Modified Files
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src/backend/access/common/heaptuple.c | 21 ++++++++++-----------
src/backend/access/common/tupdesc.c   | 18 +++++++++---------
src/backend/utils/cache/relcache.c    | 10 +++++-----
src/include/access/tupdesc_details.h  |  5 ++---
4 files changed, 26 insertions(+), 28 deletions(-)